added debug logs and code to assert that we are in the gui thread

src/util/assertinguithread.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <QCoreApplication>
+#include <QThread>
+#include <cassert>
+
+namespace chatterino {
+namespace util {
+
+void assertInGuiThread()
+{
+#ifdef _DEBUG
+    assert(QCoreApplication::instance()->thread() == QThread::currentThread());
+#endif
+}
+
+}  // namespace util
+}  // namespace chatterino